Role of MRI in the Evaluation of Abdominal Tuberculosis

Introduction:

Despite various therapeutic and diagnostic advances, tuberculosis remains a grave concern, particularly in developing countries. It is an infectious disease frequently associated with poverty, immunodeficiency, and inferior quality of life. Tuberculosis is a global epidemic that accounts for relatively high morbidity and mortality rates. Imaging techniques are crucial to diagnose the condition, assess the extent of the disease, and their response to therapy. Early diagnosis ensures prompt treatment, thereby significantly improving the outcome.

What Is Tuberculosis?

Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis. It mainly affects the lungs but can also be found in other body parts such as bone, brain, abdomen, and reproductive organs. Lung tuberculosis is an air-borne disease and is considered the most contagious type. Though TB is potentially fatal, early diagnosis and prompt treatment promise a complete recovery. Tuberculosis exists in two forms, a latent form, where the immune system is strong enough to keep the infection in check and is not contagious. The second form is the active disease which is symptomatic and are contagious.

What Are the Types of Tuberculosis?

Tuberculosis can be categorized into various types depending on the organ affected. They can be broadly classified into two types; pulmonary and extrapulmonary. They are described below:

• Pulmonary Tuberculosis: This is a primary form that affects the lungs.

• Extrapulmonary Tuberculosis: When organs other than the lungs are affected, it is known as extrapulmonary tuberculosis. They can be of the following types:

• Lymph Node Tuberculosis: Affecting the lymph nodes.

• Skeletal Tuberculosis: Affecting the bones.

• Genitourinary Tuberculosis: Affecting the genitals, urinary tract, and kidneys.

• TB Meningitis: Affecting the brain and spinal cord.

• Gastrointestinal Tuberculosis: Affects the digestive tract and the gastrointestinal system.

What Is Abdominal Tuberculosis?

Abdominal tuberculosis is the most common type of extrapulmonary tuberculosis affecting the gastrointestinal tract and abdominal organs. It can affect the intestines, liver, spleen, pancreas, peritoneum, and abdominal lymph nodes.

How Does Abdominal Tuberculosis Occur?

Tuberculosis of the abdomen may occur in the following ways:

• Consuming unpasteurized cow’s milk.

• Spread of bacteria from the lungs to the gastrointestinal tract via the bloodstream.

• Lymphatic spread from the affected lymph nodes.

• Ingestion of infected sputum.

• A direct spread from adjacent infected organs, tissues, or bones.

What Are the Types of Abdominal Tuberculosis?

Abdominal tuberculosis can be classified into the following four types:

1. Tubercular Lymphadenopathy: Tuberculosis affects the abdominal lymph nodes, primarily the mesenteric and the omental lymph nodes.

2. Peritoneal Tuberculosis: Tuberculosis affects the peritoneum (tissue lining the abdominal cavity).

3. Intestinal Tuberculosis: Affecting either the large intestine or small intestine. The most common site for intestinal tuberculosis is the junction where the ileum and caecum meet. It could be due to the increased lymphatic tissue in this region.

4. Hepatic Tuberculosis: Tuberculosis of the liver.

What Are the Symptoms of Abdominal Tuberculosis?

The signs and symptoms depend on the site involved. They are given below:

• Abdominal pain.

• Loss of weight.

• Nausea.

• Fever.

• Night sweats.

• Decreased appetite.

• Diarrhea or constipation.

• Fluid accumulation in the abdominal cavity or liver.

• Bloody stool.

• Lump in the abdomen.

How Is Abdominal Tuberculosis Diagnosed?

Diagnosing abdominal tuberculosis could be challenging as the clinical features overlap with various other conditions. A delay in diagnosis could significantly increase morbidity. Hence early diagnosis and prompt treatment are crucial in abdominal tuberculosis for better patient prognosis. Diagnosis is usually made by isolating the bacteria from the abdominal tissue or peritoneal fluid. This could be retrieved either through an endoscopy or a biopsy. However, imaging tests such as X-ray, ultrasound, computed tomography, and magnetic resonance imaging (MRI) can also be used as ancillary tests to support the diagnosis and assess the treatment strategy.

What Is the Role of Imaging Modalities in Diagnosing Abdominal Tuberculosis?

Though imaging findings are not characteristic of abdominal tuberculosis, they are a vital tool in substantiating the diagnosis and assessing the response to the treatment. They are described below:

1. Ultrasound:

Studies have proved abdominal ultrasound to be 63 % sensitive and 68 % specific in diagnosing abdominal tuberculosis. Hence a negative ultrasound does not rule out the possibility of abdominal TB. A few of the characteristic findings in ultrasound are:

• Fluid accumulation in the abdomen.

• Enlarged lymph nodes.

• Lesions in the liver, spleen, or pancreas.

2. Computed Tomography:

The paradigm shift in diagnostic advances revolutionized the role of computed tomography (CT) in diagnosing tuberculosis. Three-dimensional imaging techniques and high-resolution images of CT aid in accurate diagnosis, especially in gastrointestinal tuberculosis. Multidetector computed tomography (MDCT) and contrast CT is more specific than conventional CT in abdominal tuberculosis. In contrast, CT demonstrates three patterns particular to abdominal tuberculosis. They are:

• Hypodense centers of the lesion with peripheral enhancement.

• Homogeneous or inhomogeneous enhancement.

• Lymph nodes showing peripheral enhancement with hypodense centers (suggesting necrosis or death of tissue).

Other patterns suggestive of abdominal tuberculosis are:

• Lymph nodes merge to form a conglomerate mass with areas of necrosis.

• Calcified lymph nodes.

• Enlarged mesenteric or omental lymph nodes.

• Bowel wall thickening.

• Peritoneal thickening with an accumulation of fluid in the peritoneal cavity.

Though these findings may also be observed in other conditions such as malignancy, inflammatory diseases, and certain other infections, correlation with clinical features can confirm the diagnosis of abdominal tuberculosis.

3. Magnetic Resonance Imaging:

MRI is superior to CT due to increased soft-tissue resolution and superior image quality. MRI is beneficial even to determine the functioning ability of the digestive tract and hence is a vital diagnostic aid in intestinal tuberculosis. However, certain artifacts caused due to respiratory movement and intestinal peristalsis, and prolonged image acquisition time limit the use of MRI. The characteristic finding of abdominal tuberculosis in MRI is a conglomeration of lymph nodes with homogenous peripheral or central areas of enhancement (which appear bright in MRI). Therefore, MRI is considered more sensitive in diagnosing abdominal tuberculosis as the lymph node enhancement and necrosis are better visualized in contrast to MRI than conventional CT.

Conclusion:

Tuberculosis is an infectious disease that presents with an array of clinical symptoms. The disease can be completely cured if diagnosed early. Delayed diagnosis not only results in a poor prognosis but can also be fatal. Though laboratory culture and biopsy are vital diagnostic aids, imaging techniques act as ancillary tools to support and confirm the diagnosis. They are essential to detect the extent of damage and associated abnormalities and even to strategize and monitor the treatment response.